Quantified Walking ability analysis

Walking is an essential activity for all human beings. It allows autonomous, independent movements. However, it is also a complex activity, requiring several years of learning before being fully efficient. Once it reached its maturity, it becomes an automatic activity that no longer requires particular attention for any of the movements forming a repeated cycle. The automation of this activity made the surveys easier, measuring and establishing bio-mechanical standards within the three dimensions of normal walk. Theses standards are essential to study a movement because they allow comparisons with patients suffering from a pathology.

Quantified Walking ability analysis thus allows three dimensional surveys of a pathologic walk and a comparison with pre-established standards.

During a quantified walking ability analysis, kinematic, kinetic and electromyographic variables are monitored. Additionally, we can complete the quantified walking ability analysis with energy expenditure measurements during the walk.

Kinematic variables allow a description of the movement and especially moving, speed and linear acceleration of the different body segments. The movements of the different body segments are monitored with an optico-electronic made of 6 infrared cameras. These cameras will locate and follow three dimensional movements of reflective beacons stuck on specific body parts. By linking the dots, we obtain a linear representation of the movements of the different body segments. From the calculations made on the movements, we can quantify linear and angular moves of each segment and determine, through consecutive integrations, the different speeds and accelerations.

Kinetic variables allow a survey on forces used to create a movement. To achieve this, we use platform that will allow the calculation of moments (defined by the force multiplied by the distance between the force vector and the articulation center) for each articulation and of powers (defined by the articulation moment multiplied by the angular speed) that are developed, thanks to previously measured kinetic data.

Kinematic and kinetic data are pictured in curves that are compared to standards, as explained above.

Electromyographic data are gathered through surface electrodes stuck on the skin, recording muscle activity moments during a walking cycle. By comparing the recorded activity pattern to standards, it is possible to determine which muscles have a deleterious activity during the walking cycle. Electrodes implanted into muscles can be used to record deeper muscles electrical activity (posterior tibial, ilio-psoas) or the activity of different chiefs of the same muscle (quadriceps for example) to locate the chief with abnormal activity.

All these data allow us to quantify the bio-mechanical data related to the walk and allow us to identify with relative precision the abnormalities as well as the muscles which inappropriate activities lead to dysfunctions.

This way, we can define if abnormalities are related either to a muscular weakness or to spastic hypertonia or to agonistic-antagonistic muscle co-contractions leading to articular stiffness.

For some patients, these results will allow us to offer a medicinal (botulinum toxin) or surgical (intrathecal implantation of a Blacofen pump, muscular lengthening, bone relaxation osteotomy,...).

In addition to the potential for diagnostics of this examination, the quantified waling ability analysis is also a powerful way of evaluation. Indeed, we often use this examination to evaluate the possible repercussions on the ability to walk of the inactivation of one or more muscles, obtained through a neurological motor blocking or, in a lesser extent, through the injection of botulinum toxin. Once it is proved that the ability to walk is improved by such medical acts, we can give more insights for the execution of surgical acts with permanent and irreversible consequences.

Different steps of a quantified walking ability analysis:
Duration: 2 to 3 hours depending on the difficulties encountered during the recording of the examination.

  1. Clinical examination of lower limbs involved in the walk, during which the amplitude of various articulations, strength and spasticity of the different muscles are evaluated.
  2. The walk is recorded on video tape.
  3. Prepping the patient: the reflective beacons are placed on specific anatomic sites and the electrodes of the electromyograph device are stuck on the muscles that we want to monitor during the walk.
  4. Bio-mechanical data acquisition during the walk: several recordings (about ten) are necessary to calculate average results.
  5. Reconstruction of the model by the therapist to obtain and interpret kinematic, kinetic and electromyographic curves.

The energy expenditure allows us to measure how much energy is consumed during the walk. We perform the measurement of the metabolic coefficient using the classic indirect calorimetric method, in open circuit. We use a spirometer to perform those evaluations. The indirect calorimetric method consists in an evaluation of the energy expenditure based on how much oxygen is consumed and how much carbon dioxide are produced during the physical effort. This method is based on the fact that, during a physical effort, the ensemble of chemical reactions producing energy results in the oxidation of carbon and hydrogen atoms and their transformation into carbon dioxide and water. In physical effort physiology, the spirometry is often performed in open circuit with the patient breathing ambient air with a constant composition (20,93% of oxygen, 0,03% of carbon dioxide, 79,04% of nitrogen and inert gas). The measurement of the ventilatory expiratory flow and the concentration of O2 and CO2 in the expired gas determines the consumption of O2 and the production of CO2.

In our laboratory, we use a spirometer with O2 analyzing paramagnetic device (Quark, Cosmed, Italy, Polar) that cannot be moved and requiring that the analysis is made on a cyclo-ergometer or on a conveyor.